Field
Exemplary embodiments of the present disclosure relate to a direct current (DC)-DC converter of a vehicle, and more particularly, to an apparatus and a method for preventing a reverse current in a DC-DC converter of a vehicle, which are capable of preventing a reverse current from being generated in a DC-DC converter of a vehicle.
Discussion of the Background
A conventional electric power flow of a hybrid vehicle will be described with reference to FIG. 1.
FIG. 1 is a diagram for describing an electric power flow of a battery system of a conventional hybrid vehicle.
As shown in FIG. 1, when a hybrid vehicle runs normally, an electric motor is driven by receiving electric power from a high voltage battery through an inverter.
The driven electric motor delivers power to a power distributor to drive an engine so that the hybrid vehicle may run. A low voltage DC-DC converter (LDC) connected to the high voltage battery may charge a low voltage battery (a 12 volts (V) battery) to supply the electric power to low voltage electronic equipment loads in the hybrid vehicle.
When the hybrid vehicle reduces speed and runs on a downhill road (a downward grade) section, a rotational force is generated at the power distributor. With such a rotational force, the electric motor may operate as an electric power generator to charge the high voltage battery through the inverter. At this point, the LDC connected to the high voltage battery may charge the low voltage battery the same as when the hybrid vehicle runs normally, thereby supplying the electric power to the low voltage electronic equipment loads in the hybrid vehicle.
A configuration of a DC-DC converter generally provided in a hybrid vehicle is the same as shown in FIG. 2.
As shown in FIG. 2, a DC-DC converter 20 may include a high voltage H-bridge circuit 21 which controls a high voltage to be applied to a main transformer 22 for a predetermined time, and the main transformer 22 for an electrical insulation.
A synchronous rectification circuit 23 is included at a secondary side of the main transformer 22 to rectify an alternating current (AC) voltage. At this point, the synchronous rectification circuit 23 may employ a metal oxide semiconductor field effect transistor (MOSFET) to increase efficiency of a battery system of a hybrid vehicle.
Further, the low voltage (for example, 12V) rectified in the synchronous rectification circuit 23 is supplied to an electronic equipment load 25 and a low voltage battery 26 (for example, a 12 V battery) via an output filter circuit 24.
In addition, a voltage control device 27 is configured as an electric power circuit of such a DC-DC converter 20 to control an output voltage. The voltage control device 27 determines a supply voltage value V3, which is supplied to the high voltage H-bridge circuit 21, according to a difference between an output voltage value V1 of the DC-DC converter 20 and a preset reference output voltage value V2.
An output voltage of the DC-DC converter 20 is controlled in real time according to various conditions of the electronic equipment load 25 of the hybrid vehicle. When the electronic equipment load 25 is abruptly changed, there is a need to limit an output current or output electric power, and a situation may arise in which the output voltage of the DC-DC converter 20 should be abruptly decreased. At this point, the reference output voltage value V2 of the DC-DC converter 20 is adjusted to be low so that a supply current being supplied to the DC-DC converter 20 may be small.
When the output voltage of the DC-DC converter 20 is lower than that of the low voltage battery 26, the DC-DC converter 20 of a synchronous rectification type may operate as a bidirectional DC-DC converter. As a result, a reverse current Iout of several hundred amperes (A) is generated at the DC-DC converter 20 in a direction as shown in FIG. 3A. For example, as a simulation result shown in FIG. 3B, when the reference output voltage value V2 of the DC-DC converter 20 is abruptly varied, a reverse current Iout of about 600 A flows at the DC-DC converter 20. Such generation of the reverse current induces burning of a circuit and is also a cause of shortening a battery lifespan.